L15: Development Of Urinary System

Question 1

Development of urinary system

Answer 1

Intermediate mesoderm —> Urogenital ridge —> Nephrogenic cord
—> Pronephros, Mesonephros, Metanephros

1. Mesonephric duct —> Ureteric bud —> Ureter
2. Metanephric blastema + Ureteric bud —> Kidney
3. Allantois (Vesicoureterocanal) + Vesical urogenital sinus (mesonephric duct) —> Urinary bladder
   4.
   Primitive bladder elongation —> Female urethra
   Proximal mesonephric duct + urogenital sinus —> Male urethra

Question 2

Development of Nephros

Answer 2

Pronephros (nonfunctional, primitive):

• 4 week
• 7-10 solid cell at 5th-7th cervical somite (cervical region)
• Run caudally —> Cloaca

Mesonephros (Interim kidney)

• 4-5 week (during regression of pronephros)
• 14-26th cervical-lumbar somite (upper thoracic to upper lumbar region)
• consists of
  1. Mesonephric tubules
  2. Mesonephric ducts
  3. Nephrogenic cord
• flow: Dorsal aorta —> glomeruli —> mesonephric tubule —> mesonephric duct
• Females: disappear by 16 week
• Males: persist as Ductus deferans

Metanephros (Permanent kidney)

• early 5th week, functional by 10th week
• 2 sources, both from Intermediate mesoderm:
  1. Ureteric bud (drainage system, metanephric diverticulum, outgrowth of distal mesonephric duct)
  2. Metanephric Blastema (nephron units, mass of intermediate mesoderm, caudal part of nephrogenic cord)

Overall: cranial regress —> distal differentiate
Mesonephric duct —> Ureteric bud —> collection
Nephrogenic cord —> Metanephric blastema —> excretion

Question 3

Development of Ureteric bud

Answer 3

由內生向外:

1-4th order: Major and minor calyces
5th order: Papillary duct / Collecting duct
6-15th order: Collecting tubules (接駁metanephric blastema的distal convoluted tubule)

Question 4

Development of Metanephric blastema (kidney)

Answer 4

1. Bowman’s capsule
2. Proximal convoluted tubule
3. Loop of Henle
4. Distal convoluted tubule (Canalise with collecting tubule from Ureteric bud)

Question 5

Interaction between metanephric blastema + ureteric bud

Answer 5

Wilms tumour 1 (WT1)
—> Sequential + Reciprocal induction of growth and differentiation
—> transform metanephric mesenchyme to epithelium
—> permanent kidneys

Disconnection between metanephric blastema and ureteric bud
—> Polycystic kidney disease
—> disrupt production of urine

Question 6

Ascend and Rotation of kidneys

Answer 6

Ascend:
Metanephros (sacral/pelvic region, supplied by middle sacral artery)
—> ascend to become Kidney (T12-L3, supplied by upper lumbar arteries)
—> Right Lobe of Liver prevent ascending of Right kidney
—> defect in ascend: horseshoe kidney, unilateral double kidney, ectopic
—> defect in arterial development: Abberant renal arteries

Rotation:
90oC forward
Hilum of kidney —> face ventrally and directs medially

Question 7

Separation of Cloaca and Allantois

Answer 7

Cloaca: divided by Urorectal septum (Separation complete by 8 week)
1. Posterior: Anorectal canal (直腸)
2. Anterior: Urogenital sinus
—> Vesical (bladder + ureter) + Pelvic + Phallic

Allantois:

1. Urachus —> Median umbilical ligament (lies between Medial umbilical ligament: fibrous remnants of Umbilical arteries)
2. Vesico-urethral canal (+ Vesical Urogenital sinus —> bladder)

Question 8

Development of urinary bladder

Answer 8

Vesicle Urogenital sinus + Vesico-urethral canal

Initially continuous with allantois:
- Allantois lumen obliterated —> Urachus (connecting apex of bladder with umbilicus) —> Median umbilical ligament (fibrous remnant of allantois) —> lies between Medial umbilical ligament: fibrous remnants of Umbilical arteries

Originally: Mesonephric duct —> Ureteric bud + Bladder wall (trigone)
Later: Ureter directly insert into bladder, separate entrance from mesonephric duct

Question 9

Perineal body

Answer 9

Between anorectum and vagina —> muscular, fascial, fibrous

—> integrity of pelvic floor (attachment for muscles)

Question 10

Trigone of bladder

Answer 10

Dilatation of mesonephric duct (mesodermal)
—> Overgrown by Cloaca and Allantois epithelium (endodermal)

Trigone: mesodermal —> eventually covered by endodermal epithelium
Bladder epithelium: endodermal

Question 11

Development of Male and Female urethra

Answer 11

Male:

• Pelvic urogenital sinus —> Prostatic + Membranous urethra
• Phallic urogenital sinus —> Penile (Spongy) urethra (endodermal)
• Glans urethra: ingrowth of ectodermal cord —> canalisation —> Spongy urethra (ectodermal)

Female:
- elongation of neck of primitive bladder (urogenital sinus) —> whole thing is endodermal

Urethral CT and smooth muscle for both male and female: Splanchnic mesenchyme (endodermal and mesodermal)

Question 12

Congenital anomalies

Answer 12

1. Kidney
—> Dysgenesis of kidney
- agenesis
- hypoplasia
- dysplasia (polycystic)
- persistent lobulation

—> Shapes and position

• Horseshoe kidney (fusion anomaly)
• Rosette
• Unilateral double kidney
• Aberrant renal arteries
• Ectopic kidney

—> Wilms tumour
- incomplete mesenchymal to epithelial transformation (WT1: signal to transform from metanephric mesenchyme to epithelial tissue)

2. Ureter
   - Bifid ureter
   - Double pelvis of ureter
   - Ecotopic orifice
   - Ureterocele (sac like pouch formed by ureter ballooning at opening in bladder)
   - Atresia
3. Bladder
   - exstrophy
   - patent urachus (cyst, sinus, fistula)
4. Urethra
   - Meatus stenosis
   - Hypospadias (opening on underside/ventral penis)
   - Epispadias (open on dorsal penis, associated with exstrophy of bladder)